Powder metallurgy aluminum parts

ABSTRACT

A powder metallurgy aluminum article and a method of producing it in which a lubricant is mixed with an aluminum powder of selected particle shape and size and the mixture is cold compacted to a desired density. The compacted mixture is then sintered in air or a protective atmosphere. The sintered article may then be coined or sized.

States atettt n91 Feb.12,1974

[54] POWDER METALLURGY ALUMINUM PARTS [75] Inventor: Sherwood W. McGee, Lisle, ll].

[73] Assignee: Amsted Industries, Inc., Chicago, Ill.

[22] Filed: Feb. 3, 1971 [21] Appl. No.: 112,242

[52] US. Cl 29/1825, 75/200, 75/206, 75/211, 75/212, 75/221, 75/224 [51] Int. Cl. B22f 3/00, B22f 7/00 [58] Field of Search..... 75/206, 211, 212, 224, 221; 29/1825 [56] References Cited UNITED STATES PATENTS 3,394,000 7/1968 Gualandi et al. 75/206 3,578,443 5/1971 Grant et al 75/206 3,619,894 11/1971 Gualandi et a1, 75/206 FOREIGN PATENTS OR APPLICATIONS 799,973 8/1958 Great Britain 75/211 Primary ExaminerBenjamin R. Padgett Attorney, Agent, or Firm-Alexander, Speckman & Staples [57] ABSTRACT A powder metallurgy aluminum article and a method of producing it in which a lubricant is mixed with an aluminum powder of selected particle shape and size and the mixture is cold compacted to a desired density. The compacted mixture is then sintered in air or a protective atmosphere. The sintered article may then be coined or sized.

6 Claims, 1 Drawing Figure POWDER METALLURGY SUMMARY OF THE INVENTION This invention is directed to, a powder metallurgy aluminum article and to a method of producing it.

An object of this invention is a powder metallurgy aluminum article of suitable tensile strength and ductility which may be produced by cold compaction and sintering.

Another object is a powdered aluminum article which does not adhere to punches and dies during compaction thereof.

Another object is a powdered aluminum article which is not subject to seizing and galling during compaction thereof.

Another object is a powdered aluminum article containing a lubricant, which article may be sintered after compaction.

Other objects may be found in the following specification, claims and drawing.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a somewhat diagrammatical representation, greatly enlarged, of a partial cross-section of the aluminum powder and the die wall after compaction of the powder.

DESCRIPTION OF THE PREFERRED EMBODIMENT Previous attempts to form useful aluminum articles by compacting and sintering aluminum powders have not been completely successful either physically or economically. These attempts failed because aluminum powders are reactive and highly weldable when their oxide films are abraded, which occurs during compaction. Although an oxide film forms almost instantaneously on the exposure of pure aluminum to air, it will not form quickly enough to prevent the particles of aluminum powder from welding to punches and dies when the oxide film is removed from the particles by the punches and dies. The welding of the aluminum particles builds up deposits of metallic aluminum on the punches and dies, resulting in heavy scoring, galling and die seizure. It is known that lubricants such as waxes and metallic soaps can be added to aluminum powder to prevent the build up of aluminum on punches and dies but the addition of such substances has prevented the sintering of the particles comprising the aluminum powder. Sintering is necessary at a later stage of the process.

It has been determined that by selection of aluminum powders of particular particle shapes and sizes and selection of particular types of waxes, the problems of seizing and galling previously connected with the build up of aluminum on compaction tools can be overcome without interfering with the sintering of the aluminum particles to one another. The aluminum powders used may be entirely aluminum or they may be blended with up to 5% copper or tin powder.

The sintering of particles of aluminum is facilitated by the mechanical abrasion of the oxide films from the particles during compaction. Mechanical abrasion is enhanced through the use of aluminum particles of geometrical shapes which provide cutting edges to break through the oxide films on the particles and thereby provide nucleation sites or aluminum to aluminum contacts for subsequent sintering between the particles.

Atomized aluminum powder formed of particles of various irregular shapes is available, including such shapes as irregular teardrop, rice grain, cylinder and plate. Almost any particle shape except spherical is desirable for use in connection with the process of this invention. A mixture of irregular shaped particles and spherical particles may be used but because it is desirable to provide as many sharp edges as possible to cut the oxide film on the particles, better results are obtained as the percentage of spherical particles in a mixture is reduced.

In addition to using aluminum particles having irregular shapes, it is also advantageous to control the size of the aluminum particles. It has been found that aluminum powders containing particles of a size finer than 200 mesh U.S. standard screen scale series do not function as satisfactorily as powders containing particles of larger sizes. Particles smaller than 200 mesh tend to fit in the clearances between the die and punch and remain to cause galling. Particles smaller than 200 mesh also contain a higher proportion of oxide film to unoxidized aluminum than do larger particles and therefore do not sinter as readily as the larger particles. The smaller particles also fill the interstices between larger particles of aluminum and tend to spring back to their original shape after compaction. This action of the particles tends to laminate the pressed body after compaction. I The following tables indicate typical cumulative Screen Analysis of atomized aluminum powder:

TYPICAL CUMULATIVE SCREEN ANALYSIS ATOMIZED ALUMINUM POWDER OF REYNOLDS METAL COMPANY Grade LS 929 Grade LSA 29 +l00 MESH 0% +14 MESH 0% +200 MESH 35% +20 MESH 5% +230 MESH 43% +30 MESH 15% +270 MESH 52% +40 MESH 99% +325 MESH 325 MESH 35% +50 MESH 100% +200 M ESH l00% The number following a plus mesh size indicates the percent of the particles retained on that screen and pre ceeding screens. The number following a minus mesh size indicates the percent of particles passing through the screen.

It has been found desirable in certain instances to add aluminum oxide or other refractory grained powders to the aluminum powders. The aluminum oxide has a scourifying effect on the oxide films of the aluminum particles and is especially desirable in powders where particles of smaller than 200 mesh size are used. The addition of aluminum oxide or other refractory grain powders also reduces galling because the oxide acts on the tool surfaces to remove aluminum that has been welded to these surfaces.

The purpose of the lubricant is to coat the tool surfaces and protect them during compaction. The lubricants should not coat the aluminum particles to any substantial extent. Also, the lubricant should not chemically oxidize the aluminum particles when the compacted particles are heated during the burn-off period of the heating cycle before sintering takes place. Satisln the following examples, in which different mixtures of aluminum powder were used, the lubricant was mixed with the powder and blended for approximately 10 minutes. The resulting mixtures were compacted factory lubricants include both Ordinary and Chlori- 5 under various pressures ranging from 5 to l7.5 t.s.i. nated hydrocarbon waxes. The lubricant used in the ex- (ton er quare inch) to densities ranging from 2.4 to amples listed is a synthetic wax sold under the trade- 2,47 gm/cc. The compacted product thus formed w mark ACRAWAX y Glyco Chemicals, New heated for twenty minutes at 700F. in a box, forced air York, New York. Other suitable lubricants include convection type furnace to burn off the lubricant. The CYNDAL sold by E.F. Houghton Company and product was then sintered for sixty minutes at l,200F. butyl stearate, common technical grade. by raising the temperature in the same furnace. Some After the aluminum powder is mixed with the lubriof the products made were then dipped in a lubricant cant, it is compacted to densities of about 2.5 gm/cc or of butyl stearate fluid, technical grade, and coined to higher and the lubricant is burned off in a box, forced a density of 2.62/2.67 gm/cc under 30 t.s.i. pressure. air convection type furnace for twenty minutes at After coining, some of the products were resintered. 700F. the aluminum powder mixture is then sintered Although many examples may be furnished, there are for sixty minutes at 1,200F. In the following examples, t ut b low typical examples in which aluminum th atmosphere d was ai[ However, latmopowders of different compositions were used. Obvispheres such as dry hydrogen, dissociated ammonia or other examples m y be and mvemlon b i i compound may b d Ai atmosphere i is not limited to the particular examples set out below preferred for the burn off portion of the heating cycle. to the Precise Proportions, temperatures and sinter- The ductility of air sintered aluminum appears to be 'ady The l Elven for Pomofls, T"- equate giving approximately 5 percent or more tensile Pacnon Pressures densltfes p -"F f heatlng elongation Simering in a dry hydrogen atmosphere cycles have all been carried out and verified in practice pears to provide improved ductility Thus, for the and the valuesgiven are satisfactory and in some cases tering portion of the heating cycle either air or reduc- Preferred vanatlons ar e COItemPIaEd, and the l m atmosphere might be chosen, depending upon tion is therefore not limited to the precise values given. nomics and properties required. I EXAMPLE 1 The drawing is a more or less diagrammatical representation of a portion of the aluminum particles and the composmon Blendmg procedure 100 peicent die wall after compaction. The larger aluminum parti- Reynolds Metal f grade a alummum cles 11 are shown flattened against one another by the i z P ifflc l ubrizant. d compressive forces of compaction. During compaction, en f Ha secon the cutting edges of the irregular shaped particles have 3 ppdrem. enslty' gm/Fc Compaction Recommendations broken and sheared away the oxide films 13 on the alu- Maximum green density: 2.47 gm/cc, obtained at 10 minum particles thereby forming nucleation sites or t aluminum to aluminum contacts 14 between the partizg j l' re S r 0 t f w u cles. The broken oxide film gathers in clusters 15 beyp lppmg p S u 51 e Recommended tool clearance: 0.002 inch maximum tween the nucleation sites. 7 H Punch/die The large number of nucleation sites between the ircoining regular? Shaped partlcles of alummun} Should be f Lubricant: butyl stearate fluid, technical grade, dip pared with the small number of such sites or aluminum parts g a conilacts l4 getween the sphe ncal Maximum coined density: 2.62/2.67 gm/cc under 30 0 es e sma er num er of such sites is due to a pressure Mechanical properties (Typical) Part Type Condition Density Tensile Hardness Elong. Crush Strength Tensile Bar As Sintered 2.45gm/cc 5,770psi 0.79% Tensile Bar As Coined 2.5Bgm/cc 8,000psi H 1.2% Tensile Bar Coined Resinter 2.58gm/cc 6,500psi H30 35% Gear Bushing+ Sintered and 2.55gm/cc K=9,500 2321b.

Coined Bushing+ Sintered, 2.55gm/cc K=9,400 2341b.

Coined Resintered +Bushing dimensions; 0.688"OD. 0.432"lD, 0.833" Long lack of cutting edges on the spherical particles to shear Stripping P from coining tools: of and break the oxide films 19 formed on the spherical Sldewan- M" g particles.

The wax particles 21 form a film on the surface 23 of the die to protect the surface against the adherence of particles of pure aluminum, such as particles 25 shown in the drawing.

EXAMPLE II Composition and Blending Procedures 66.6 percent Reynolds Metal Company, grade LSA-29 aluminum Mechanical properties (Typical) Part Type Condition Density Tensile Hardness Elong. Crush Strength Tensile Bar As Sintered Tensile Bar As coined 2.62 IOOOpsi IORH 2.0% Tensile Bar Coined Resinter 2.62 l500psi 8RH 1.5% Gear Bushing+ As Sintered 2.36 K=4,900 llolh.

and coined Bushing+ Sintered,

Coined Resintered 2.36 K=6.200 1461b.

+Bushing Dimensions; 0.688"OD. 0.432"lD, 0.833" Long powder and 33.3% grade 1-842 aluminum powder plus one-half percent Acrawax C lubricant.

Typical Stripping Pressure: 0.35 t.s.i. of sidewall. Recommended Tool clearance 0.002 inch maximum Blending time: 10 minutes. Hall flow: oversized (6 punch/die minutes with assist) Coining 7 Mechanical properties (Typical) Part Type Condition Density Tensile Hardness Elong. Crush Strength Tensile Bar As Sintered 2.44gm/cc 1,187psi RH 0.5% Tensile Bar As Coined 2.62gm/cc 1,974psi 20RH 0.5% Tensile Bar Coined Resinter 2.63gm/cc 2,407psi 20RH Gear+ As Sintered 2.49gm/cc 20RH 29llb. Bushing++ As Sintered 2.33gm/cc K=2,900 20RH 58lb.

+Gear dimensions; 11 tooth spur, 1.125" root circle, 0.600"ID, 0.575"thick. HBushing dimensions; 0.548"OD. 0.298"1D, 0.515" long.

EXAMPLE III Composition and Blending Procedure: 100 percent Reynolds Metal Company grade l-842 aluminum powder plus 1.0 percent Acrawax C lubricant.

Blending time: 10 minutes. Hall flow: 11.0 seconds, Apparent density 1.17 gm/cc. Compaction Recommendations Maximum Green Density: 2.45 gm/cc obtained at 10 t.s.i., compaction.

Lubricant: butyl stearate fluid, technical grade, dip parts.

Maximum Coined density: 2.62/2.67 gm/cc under 30 t.s.i. pressure Stripping Pressure from Coining tools: 0.53 t.s.i. of sidewall EXAMPLE IV Composition and Blending Procedure: Composition 98.0 Reynolds Metal Company grade 1-511 aluminum powder and 2.0% A1 0; (240 Grit) and 2.0 percent Acrawax C lubricant.

Blending time: 10 minutes. Hall flow: 10 minutes (with assist). Use cps feed shoe vibration with Syntron unit.

Apparent density 1.03gm/cc Compaction Recommendations:

Maximum Green Density: 2.45 gm/cc obtained at 17.5 t.s.i. compaction Typical Stripping Pressure: 0.80 t.s.i. of sidewall (30 t.s.i. compaction) Recommended Tool Clearance: 0.002 inch maximum punch/die Coining Lubricant: butyl stearate fluid, technical grade, dip

parts.

Maximum Coined Density: 2.62/2.67 gm/cc under 30 t.s.i. pressure Mechanical properties (Typical) Part Type Condition Density Tensile Hardness Elong. Crush Strength Tensile Bar As Sintered 2.45gm/cc 9,742psi 0.57%

Tensile Bar As Coined 2.64gm/cc 13,659psi 0.27%

Tensile Bar Coined Resinter 2.63gm/cc l2,6l9psi 0.99%

(ieur+ As Sintered 2.20gm/cc 409lb.

Gear+ As Sintered 2.45 gmlcc 713lb.

+ Gear dimensions; ll tooth spur, 1.150" P.D. (approx.), 0600""). 0.575" thick.

I claim: 1. in a method of making a powder aluminum part having excellent aluminum to aluminum bond between contacting particles from commercial aluminum powder, the steps of providing, as a starting material, powder from th group consisting essentially of 1) commercial aluminum powder containing the usual impurities, (2) a mixture of said commercial aluminum powder with up to percent commercial copper powder or 5 percent commercial tin powder, and (3) said commercial aluminum powder with either commercial aluminum oxide powder or other commercial refractory grained powders, at least the aluminum powder portion of said starting material being further composed of irregular shapes or a mixture of irregular and spherical shaped particles, whereby sharp edges are provided for cutting oxide films on the aluminum powders, adding to the above described powder a lubricant capable of coating compaction tool surfaces and incapable of chemically oxidizing the aluminum particles during subsequent heating and sintering, compacting the powder-lubricant mixture to a density of about 2.5 gm/cc, heating the compacted powderlubricant mixture at a first temperature to remove the lubricant, and heating the compacted powder mixture at a second temperature which is higher than said first temperature to sinter said compacted powder mixture. 2. The method of claim 1 further characterized in that at least a portion of the heating step is performed in an atmosphere selected from the group consisting essentially of air, dry hydrogen, disassociated ammonia, and a carburizing compound. 3. The method of claim l further characterized in that the aluminum powder consists of particles no finer than 200 mesh US. Standard screen scale series. 4. The method of claim 1 further characterized in that the powder-lubricant mixture is subjected to a temperature of about 700F, and, thereafter, the resultant compacted powder mixture is subjected to an elevated temperature treatment of about 1,200F for about one hour to thereby sinter the compacted powder. 5. The method of claim 1 further including the steps of lubricating the sintered compacted powder mixture,

coining, and, optionally, re-sintering. 6. An aluminum powder metallurgy article having excellent aluminum to aluminum bond between contacting aluminum particles made by the following method:

providing, as a starting material, powder from the group consisting essentially of (1) commercial aluminum powder containing the usual impurities, (2) a mixture of said commercial aluminum powder with up to 5 percent commercial copper powder or 5 percent commercial tin powder, and (3) said commercial aluminum powder with either commercial aluminum oxide powder or other commercial refractory grained powders,

at least the aluminum powder portion of said starting material being further composed of irregular shapes or a mixture of irregular and spherical shaped particles, whereby sharp edges are provided for cutting oxide films on the aluminum powders,

adding to the above described powder a lubricant capable of coating compaction toolsurfaces and incapable of chemically oxidizing the aluminum particles during subsequent heating and sintering,

compacting the powder-lubricant mixture to a density of about 2.5 gm/cc,

heating the compacted powder-lubricant mixture at a first temperature to remove the lubricant, and

heating the compacted powder mixture at a second temperature which is higher than said first temperature to sinter said compacted powder mixture,

said article having a tensile strength of from about 1,200 to 10,000 psi in the as-sintered condition. 

2. The method of claim 1 further characterized in that at least a portion of the heating step is performed in an atmosphere selected from the group consisting essentially of air, dry hydrogen, disassociated ammonia, and a carburizing compound.
 3. The method of claim 1 further characterized in that the aluminum powder consists of particles no finer than 200 mesh U.S. Standard screen scale series.
 4. The method of claim 1 further characterized in that the powder-lubricant mixture is subjected to a temperature of about 700*F, and, thereafter, the resultant compacted powder mixture is subjected to an elevated temperature treatment oF about 1,200*F for about one hour to thereby sinter the compacted powder.
 5. The method of claim 1 further including the steps of lubricating the sintered compacted powder mixture, coining, and, optionally, re-sintering.
 6. An aluminum powder metallurgy article having excellent aluminum to aluminum bond between contacting aluminum particles made by the following method: providing, as a starting material, powder from the group consisting essentially of (1) commercial aluminum powder containing the usual impurities, (2) a mixture of said commercial aluminum powder with up to 5 percent commercial copper powder or 5 percent commercial tin powder, and (3) said commercial aluminum powder with either commercial aluminum oxide powder or other commercial refractory grained powders, at least the aluminum powder portion of said starting material being further composed of irregular shapes or a mixture of irregular and spherical shaped particles, whereby sharp edges are provided for cutting oxide films on the aluminum powders, adding to the above described powder a lubricant capable of coating compaction tool surfaces and incapable of chemically oxidizing the aluminum particles during subsequent heating and sintering, compacting the powder-lubricant mixture to a density of about 2.5 gm/cc, heating the compacted powder-lubricant mixture at a first temperature to remove the lubricant, and heating the compacted powder mixture at a second temperature which is higher than said first temperature to sinter said compacted powder mixture, said article having a tensile strength of from about 1,200 to 10,000 psi in the as-sintered condition. 